1. Field of the Invention
The present invention relates generally to a light scattering type smoke sensor and more particularly to sensing scattered light caused by smoke particles flowing from the outside into the smoke detection chamber to detect a fire.
2. Description of the Related Art
There is a prior art conventional light scattering type smoke sensor as shown in FIG. 4. FIG. 4(A) shows the lower part of the sensor main body 100 of a sensor equipped with a cover 102 and the smoke detection chamber 103 where smoke flows into the interior section. The sensor main body 100 includes a holder 104 mounted inside the smoke detection chamber 103. The light emitting part 106 and light detecting part 108 are contained within the holder 104 and positioned in proximity to opening 110 and opening 112, respectively.
FIG. 4(B) shows the light emitting part 106 radiating light in the direction of optical axis 114. The monitoring of scattered light caused by the influx of smoke is carried out in the light detecting part 108 from the direction of optical axis 116.
The light emitting part 106 and the light detecting part 108 are disposed so optical axis 114 intersects with optical axis 116 on an imaginary horizontal plane. The scattering angle θ of optical axis intersecting point 118 employs a predetermined setting. At this point the intersecting angle δ of the optical axis supplements the scattering angle θ to determine the configuration angle with the referential of θ=180°−δ.
Furthermore, a light barrier is employed consisting of shielding plate 120 and shielding plate 122. Shielding plate 120 blocks light from passing directly through to the light detecting part 108. Residual direct light reflected from the front side of shielding plate 120 is further reduced by the back shielding plate 122.
Additionally, in this conventional structure as shown in FIG. 4(A), the optical axis of the light emitting part 106 and the light detecting part 108 are arranged at downward grade of about 3˜5 degrees, and the optical axis intersecting point is adjusted so that it will not be too close to the upper surface of the smoke detection chamber 103.
However, in this type of conventional light scattering type smoke sensor, as the light emitting part 106, light detecting part 108, shielding plate 120 and shielding plate 122 protrude into the smoke detection chamber 103 where the smoke flows in, the possibility of a problem with the directivity in the influx of smoke from the outside is high.
FIG. 5 shows a prior art light scattering type smoke sensor which is designed not to have directivity in the smoke inflow to the smoke detection chamber 103.
In FIG. 5, the sensor main body 200 is comprised of a cover 202 and a smoke detection chamber 203 into which smoke flows into the main interior cavity. The smoke detection chamber 203 in the sensor main body 200 includes a holder 204, a light emitting part 206 and a light detecting part 208 embedded within opening 210 and opening 212 in holder 204, and thus the structure does not have directivity in the inflow of smoke.
The light emitting part 206 gives off scattered light in the direction of optical axis 214, and the light detecting part 208 subjected to light is located in the direction of optical axis 216. For this reason, on the imaginary vertical plane inside the sensor, the slanting downward arrangement of optical axis 214 and optical axis 216 are positioned so that the light emitting part 206 and the light detecting part 208 are not facing each other. The scattering angle θ of optical axis intersecting point 218 is set at a predetermined angle. In addition, the configuration angle δ has the relation of θ=180 degrees−δ.
On the other hand, as for the type of smoke produced by a fire, the diameter of smoke particles vary from comparatively large to small depending on the burning material. For this reason, let it be one subject there be no difference in the various diameters of smoke particles in respect to sensitivity as much as possible.
It is known that the smoke particle diameter relative to a scattering angle θ of about 60˜90 degrees results in the least sensitivity difference (a configuration angle δ90˜120 degrees) (Japanese Laid-open Kokai Patent Publication (1995) No. Heisei 7-72073).
However, in the conventional structure shown in FIG. 5, if the scattering angle θ is enlarged to about 60 degrees to lessen the sensitivity difference over the diameter of smoke particles, the optical axis intersecting point 218 drops downward from the installation side holder 204. Consequently, as the vertical side of the scattering angle θ cannot be made into a suitable angle range of 60˜90 degrees and to avoid the influence of reflected light from the ceiling side, the height of the sensor (smoke detection part) must be enlarged.
In this case, although a thin-shaped smoke sensor is possible if the interval of the light emitting part 206 and the light detecting part 208 are narrowed to form a scattering angle θ of 60˜90 degrees, the problems of electrical induction to the light detecting part or the influence of unacceptable direct light leaking through occurs. Therefore, since it is necessary to separate the light emitting part and the light detecting part as much as possible, along with maintaining a scattering angle θ of 60˜90 degrees without changing the height of the smoke detection chamber, a sensor with a thin-shaped smoke detection part cannot be made.
The purpose of this invention constitutes a thin-shaped smoke detection part, which enables the setup of a scattering angle with no directivity in the smoke influx to the smoke detection chamber.
Furthermore, the light emitting part and light detecting part of the smoke scattering senor are arranged to keep them separated as much as possible to block out direct light.